Determining the direction and/or intensity of vibrations provides valuable information in many diverse technological fields, for example, seismic plotting of an earthquake, locating tunnel activity, and intrusion event detection.
A common prior art vibration sensor comprises a transducer in contact with fluid in a chamber. As the fluid vibrates in response to vibrations that contact the chamber, the transducer produces a signal that is received by a signal interpreter. The interpreter uses the signal to characterize vibrations in magnitude, frequency or vector along an axis passing through the fluid.
To characterize a vibration in multiple axes, multiple sensors, each having a different axis, for example, are coupled together or alternatively, the sensor is rotated and/or moved with respect to the vibration; as seen in the following exemplary patents:
In U.S. Pat. No. 4,525,819, Hartley, John Edward teaches a geophone transducer that is partially submerged in a fluid and detects horizontal seismic waves.
In U.S. Pat. No. 4,334,296, Hall Jr., Ernest M. teaches a geophone comprising a fluid filled chamber having transducers in flexible top and bottom walls. Multiple geophones are used to provide output signals relating to the direction of the earth's motion.